The present invention relates generally to a bent type zoom optical system and an imaging system incorporating the same, and more particularly to a slimmed-down, small-format yet high-zoom-ratio bent type zoom optical system that can be tucked away in a lens mount and an imaging system incorporating the same.
In recent years, electronic imaging device-incorporated imaging systems like digital still cameras have caught on. With the development and increasing use of digital still cameras, there are now growing demands for higher image quality and further size reductions and, among others, there are strong demands for slimmed-down, high-zoom-ratio yet compact optical systems.
When it comes to a high-zoom-ratio optical system having a long optical length, however, it is not that slimmed down upon received or tucked away in a lens mount even by use of a lens barrel mechanism wherein the spaces between lens groups are simply narrowed down to curtail the whole length of the optical system upon received in the lens mount. To meet those demands, there are some proposals offered as set forth in Patent Publications 1 to 7.
Patent Publication 1 shows a mechanism with which some lens groups are moved back from on the optical axis and tucked away in another site in a lens barrel so that the pileup is slimmed down.
There is also an optical system or mechanism proposed, wherein a reflecting member is used in the optical axis through the lens group nearest to the object side to bend the optical path for thickness reductions, and, as in Patent Publications 2 and 3, there are an optical system and an imaging system proposed as well, wherein lenses on the object side with respect to the reflecting member are tucked away in the lens mount.
Moreover, such mechanisms as set forth in Patent Publications 4, 5 and 6 are made in the art.
Patent Publication 1
JP(A)2003-149723
Patent Publication 2
JP(A)2004-102089
Patent Publication 3
JP(A)2002-169088
Patent Publication 4
JP(A)2005-266173
Patent Publication 5
JP(A)2005-300562
Patent Publication 6
JP(A)7-168096
Patent Publication 7
JP(A)10-20191
Patent Publication 8
JP(A)11-64714
When the mechanism, with which some lens groups are moved back from on the optical axis to curtail the thickness of the optical system upon tucked away in the lens mount, is used as set forth in Patent Publication 1, the presence of a mechanism for making sure the total length of the optical system would incur a contradiction between the thickness of the optical system upon tucked away in the lens mount and an increase in the outer diameter of the lens barrel, unless the optical whole length of the optical system at the time of taking images or the amount of movement of lens groups moving for zooming is reduced. In other words, to slim down the optical system upon received in the lens mount, there is the need of shortening the length of the mechanism for moving forth and back the respective lens groups, which leads to another need of using a lot more structural parts for moving forth them a given length. Such a slimmed-down yet high-zoom-ratio arrangement as in Patent Publication 1 at the same time requires a decrease in the whole length; there is no choice but to strengthen the refracting power of each lens group, resulting in much difficulty in making sure optical performance.
With Patent Publications 2 and 3, much is still desired in view of reductions in the size of the optical system upon received in the lens mount, because an internal reflecting prism is used as the bending means.
Even with the mechanism with which, as in Patent Publication 4, the reflecting member is provided to the lens group nearest to the object side to bend the optical path, there is an obstacle to size reductions, because a high-zoom-ratio arrangement would have its whole length growing longer on the imaging plane side with respect to the reflecting member.
Patent Publications 5 and 6 come up with a lens barrel mechanism, but they do not disclose anything specific about the optical system; they do not disclose any optimum embodiment about the mechanism and optical system necessary for reducing the whole size of the lens barrel.
Patent Publication 7 proposes that the optical axis is bent 90° somewhere along the optical path for size reductions in the optical axis direction. Still, much is desired in view of size reductions of the optical system upon tucked away in the lens mount.